Optimizing-QoS-vSphere_final

ConfiguringtheLimitsValue
The Limitsvaluespeciesanabsolute
maximumlimitonegresstrafcforthat
trafctypeonahost.Limitsarespecied
inMb/s.Thelimitisanaggregateforthat
trafctypeandappliesregardlessofthe
number of physical server adapters in the
NIC team.
Note:Limitsareappliedtothenetwork
trafcbeforetheshares.Limitsapply
over a team, while shares schedule and
prioritizetrafcforeachphysicalserver
adapter.
NetIOC Usage
Unlikelimits,whicharespeciedinabsolute
unitsofMb/s,sharesareusedtospecifythe
relativeimportanceofspecicows.Shares
arespeciedinabstractunitswithavalue
ranging from 1 to 100. In this section, an
example describes the usage of shares.
Figure 12 highlights the following
characteristics of shares:
•, a
particular traffic flow gets 100 percent
of the bandwidth available, even if it was
configuredwithjust25shares.
•,
bandwidth is divided among the traffic
flows based on their relative shares.
For further details, refer to the
document, “VMwareNetworkI/OControl:
Architecture,PerformanceandBest
Practices.”
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
To enforce QoS, it is necessary to be able
to set the priority of access to central
data stores by VMs across a virtualized
environment. That is, higher-priority
requests for data must take precedence
over other types of requests to ensure
appropriate latencies. VMware vSphere 4.1
achievesthatprioritizationforspecicdata
stores using a system of shares and limits
similar to that described above for NetIOC.
The VMware vSphere 4.1 Storage
I/OControlmechanismmonitorsthe
latency associated with communication
between a VM and data store. If network
connectivity to the data store becomes
congested (the latency exceeds a
thresholddenedbytheadministrator),
the mechanism prioritizes access to the
data store according to the shares and
limitsthathavebeendenedinadvance
to meet QoS requirements.
VM Traffic (25)
Vmotion (50)
VM Traffic (25)
iSCSI (100)
Vmotion (50)
Shares Example: VM=25; Vmotion=50;iSCSI=100
VM Traffic (25)
100%
VM Traffic (25)
iSCSI (100)
20%
80%
33%
67%
14%
29%
57%
Shares values assign the relative importance to various types of traffic flows.
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